baocao final sua

8/3/2019 Baocao Final Sua

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GVHD: TS.V C LUNG SVTH: L HONG HTRN LONG KHNH

CHNG1

TMHIUVCCHTHNGNHNDNGTINGNI.

1.1t vn Ngy nay cng vi s pht trin ca khoa hc kthut, cc h thng my mc

ngy cng hon thin gip con ngi lm vic hiu qu hn v cng gii

phng con ngi trong rt nhiu cng on ca cng vic. Tuy nhin qu trnh

giao tip gia ngi v my vn cn nhiu bt cp phi thng qua cc thit b xut

nhp chun. ngy cng t nhin ho vic giao tip v iu khin my mc, vn

nghin cu cc phng php nhn dng ting ni c t ra v c mt s

phn mn ra i nhn dng ting anh tng i tt nh via voice ca IBM, spoken

toolkit ca CSLU(central of spoken language understanding),Speech Recognition

ca Microsoft

Tuy nhin i vi ting vit th cha c h thng nhn din hon chnh no

c xy dng, vn ny ch mi c quan tm nghin cu trong nhng nm

gn y. c mt s cng trnh nghin cu vlnh vc ny vi nhiu hng tip

cn khc nhau, song kt qut c vn cn nhiu khim tn(v dnh phn

mm Vspeech ca nhm Sinh Vin i hc Bch Khoa TPHCM,VN voice ca

PGS.TS Lng Chi Mai Vin Cng Ngh Thng Tin..). Do , ny sinh vn

cn xy dng mt nn tng hon chnh tm ra mt hng i thch hp cho

nghin cu nhn dng ting ni nhm t c mt kt qu tt hn.

1.2Tnh hnh pht trinVi s pht trin nhanh chng ca cc ngnh cng nghip iu khin, tng

ho, lin quan ti lnh vc ngn ng. T cn phi c s lin kt cht ch gia

cc loi ngn ng(ngn ng khoa hc,my,) lm cho vic iu khin v x

l cng vic mt cch d dng v thun tin hn. Khi lng cng vic c th

c tngln ng k nhnhng tin li trong trao i thng tin. V vy, x l

v nhn dng ting ni p dng vo cc lnh vc l yu cu cn thit c

ra.


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Trc s pht trin ca my tnh nhiu nh khoa hc ngh n vn

lm th no nhn dng c ting ni, chuyn ting ni thnh vn bn v

ngc li chuyn vn bn thnh ting ni lm cho con ngi c khnng giao tip

vi my tnh bng ngn ng v t c th giao tip vi cc thit b khc bngting ni mt cch d dng. S pht trin ca my tnh lm cho vn x l v

nhn dng tng chng nh rt d dng nhng trn thc t th khng hon ton

nh vy.

Nhng nguyn nhn xl v nhn dng ting ni trnn phc tp:

Trn th gii c rt nhiu loi ngn ng, mi quc gia, dn tc c mt

loi ngn ng ring nn rt kh to mt h thng nhn dng chung m bt k aicng c th s dng c.

Cu to thanh qun ca mi ngi cng rt khc nhau cho nn vic pht m

ca cng mt t ca nhng ngi khc nhau cng c s khc bit ln.

Nhn dng ting ni khng ch l nhn dng mt t hay mt s t m l

nhn dng mt chui cc t lin tc v cn phi xc nh cc t nhn dng c l

ng hay sai v mt ng php, ph hp vi nhng lnh thit kt hay khng, nu

khng th phi x l nh th no.

Bn thn ting ni khng n nh li c pht ra trong mi trng c

nhiu cng lm cho cc c trng ca ting ni b sai lch v snh hng trong

qu trnh nhn dng.

1.3Tnh hnh nghin cu v ng dng1.3.1Tnh hnh nghin cu nhn ging ting ni:Ngy nay trn th gii c rt nhiu nghin cu v nhn dng ting ni

trong nhiu lnh vc khc nhau vi rt nhiu phng php rt a dng. Mi h

thng nhn dng v x l khc nhau hai c im:

- c trng ting ni c tch thc hin vic x l v nhn dng.

- Phng php p dng phn bit cc c trng ca ting ni.


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Cc phng php nhn dng ting ni phbin:

Phng php ngm - m v hc (acoustic-phonetic approach)

Phng php ng m - m v hc da trn l thuyt m v: l thuyt ny khng

nh s tn ti hu hn v duy nht cc n v ngm c bn trong ngn ng ni

gi l m v, c phn chia thnh: nguyn m - ph m, v thanh-hu thanh, m

vang -m bt Cc m v c thxc nh bi tp cc c trng trong ph ca tn

hiu ting ni theo thi gian.

c trng quan trng nht ca m vl formant. l cc vng tn s c cng

hng cao nht ca tn hiu. Ngoi ra cn mt sc trng khc nh m vc (cao

-pitch), m lng

H thng nhn dng da trn phng php ny stch cc c trng t tn hiu

ting ni v xc nh chng tng ng vi m vno. Sau , da vo mt tin

phin m, my sxc nh chui cc m v c khnng l pht m ca t no

nht.

Xt kha cnh nguyn l, phng php c v rt n gin. Tuy nhin cc th

nghim trong thc t cho thy phng php cho kt qu nhn dng khng cao.Nguyn nhn t nhng vn sau:

Phng php cn rt nhiu tri thc v ng m hc, nht l cc tri thc

lin quan n c tnh m hc ca cc m v. M nhng tri thc ny

nhn chung cn cha c nghin cu y .

formant chn nh i vi cc nguyn m, vi ph m formant rt kh

xc nh v khng n nh. Hn na vic xc nh cc formant cho

chnh xc khng cao. c bit khi chu nh hng ca nhiu (l vn

thng xy trong thc t).

Rt kh phn bit cc m v da trn ph, nht l cc ph m v

thanh. C mt s ph m rt ging nhiu (v d: /s/, /h/).


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Phng php tr tu nhn to (artifactial intelligence approach)

Phng php tr tu nhn to nghin cu cch hc ni v hc nghe ca con

ngi, tm hiu cc quy lut ng m, ng php, ngngha, ng cnh v tch hp

chng bsung cho cc phng php khc nng cao kt qu nhn dng.

Chng hn c th thm cc h chuyn gia (expert system), cc lut logic m

(fuzzy logic) v ng m, m v vo cc h nhn dng ting ni da trn phng

php ng m-m v hc tng chnh xc cho vic xc nh cc m v (vn

c cp l rt kh nu ch s dng cc thng tin v m ph ).

Hay i vi cc h nhn dng mu, ngi ta ci tin bng cch vi mi i

tng cn nhn dng, h thng s chn ra mt s mu ging i tng nht, sau s kim chng tip cc kt qu bng cc lut ng php, ng ngha, ng

cnh xc nh mu ph hp nht.

Hin nay ang c mt phng php tr tu nhn to trong nhn dng ting ni

c nghin cu rng ri l mng nron. Tu vo cch s dng, mng nron c

th coi l mrng ca phng php nhn dng mu hoc phng php ng m-

m v hc.

Phng php nhn dng mu (pattern recognition approach)

Phng php nhn dng mu da vo l thuyt xc sut - thng k nhn

dng da trn tng: so snh i tng cn nhn dng vi cc mu c thu

thp trc tm mu "ging" i tng nht.

Nh vy h thng nhn dng s tri qua 2 giai on:

Giai on hun luyn thc hin cc nhim v: thu thp mu,phn lp v hun luyn h thng ghi nhcc mu .


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Ngun voThu thp, tin x

l

Trch chn ctrng

Dl

iuhu

nluyn

Mu d liu hun luynPhn lp

ctrng

Hun luyn ccu nhn dng

C cu nhn dng

Hnh 1.1 S giai on hun luyn ca phng php i snh mu

Giai on nhn dng: nhn vo i tng cn nhn dng, so

snh vi cc mu v a ra kt qu l mu ging i tng nht.

Ngun voThu thp, tin x

l

Trch chn ctrng

it

ngcnnhndng

c trngC cu nhn

dng

Thngtinphnlp

La chn lp,hu x l

Kt qu

Hnh 1.2 S giai on nhn dng ca phng php i snh mu

Phn ln cc h nhn dng thnh cng trn th gii l s dng phng php

ny. Phng php c nhng u im sau:

S dng n gin, d hiu, mang tnh ton hc cao (l thuyt xc sut

thng k, l thuyt my hc, )


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t bnh hng ca nhng bin th v b t vng, tp c trng, n v

nhn dng, mi trng xung quanh

Cho kt qucao. iu ny c kim chng trong thc t.

Nhn dng mu s dng m hnh Markov n l phng php c chn thc hin ti nn sc trnh by chi tit phn sau ca bo co.

1.3.2 Khnng ng dng:H thng nhn dng ting ni l h thng cho php u vo l ting ni con

ngi. C 3 ng dng cbn ca h thng nhn dng ting ni:

Voice commands: ngi s dng ni vo mt lnh v my tnh thc hin

mt cng vic tng ng vi lnh . Text dictation: ngi s dng c chnh t, cn my tnh s ghi li

nhng g ngi s dng c. i hi my tnh phi cho php c ton b t vng

trong ngn ng.

Speaker recognition: ngi s dng c vo mt cu cho sn v my

tnh snh danh ngi dng da trn cc c tnh ca ging ni.

1.4Tnh hnh tng quan trong v ngoi ncThgii:

Trn th gii c nhiu nh khoa hc cc trng i hc v cng ty ln u

tvo lnh vc nhn dng ting ni v c nhiu thnh tu ng k. Di y l

mt s d n nghin cu tiu biu.

CMU SPHINX: cn gi gn l SPHINX l mt h nhn dng ting

ni c pht trin ti i hc Carnegie Mellon, bao gm mt Engine nhn dng

tn l SPHINX v mt chng trnh hun luyn m v l SphinxTrain. K tnm

2001, nhm pht trin Sphinx m m ngun mt s thnh phn ca chng

trnh nhn dng bao gm Sphinx 2 v ti nay l Sphinx 4. Ngoi ra cn mt s

chng trnh khc km theo gm chng trnh hun luyn m hnh m v

(acoustic model), chng trnh bin dch m hnh ngn ng (language model) v


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t din pht m (cmudict), l cc chng trnh cn thit s dng Sphinx. Chi

tit v Sphinx c th tham kho ti a ch http://cmusphinx.sourceforge.net.

Microsoft Speech Recognition: tnm 1993 sau khi tuyn mc

ngi ng u ca nhm nghin cu Sphinx X.Huang, t i hc CarnegieMellon, Microsoft b thu ht vo lnh vc nghin cu nhn dng ting ni v

chuyn vn bn sang ting ni(text - to - speech). Cng ty ny sau xy dng

Speech API (SAPI), mt giao din lp trnh dnh cho nhng ai mun pht trin

ng dng lin quan n ging ni trn mi trng Windows. Hin ti c SAPI

5.4, chi tit c th tham kho ti

http://www.microsoft.com/speech/speech2007/default.mspx.

Julius: l mt d n m ngun m nghin cu pht trin h nhndng ting ni vi b t vng ln (khong 60000 t) da trn m hnh Markov n

ph thuc ng cnh. Mc tiu chnh ca Julius l pht trin h nhn dng ting ni

lin tc vi b t vng ln dnh cho ting Nht. y l mt chng trnh nhn

dng m ngun mc khnng nghin cu m rng cho nhiu ngn ng khc

nhau, chi tit ti a chhttp://julius.sourceforge.jp/en_index.php.

Dragon: y l mt sn phm thng mi ni ting trong lnh vc

nhp ging v tng hp ting ni c cng ty NUACE. Cng ty ny pht trinh nhn dng ca ring mnh v cho ra i nhiu phin bn Dragon khc nhau p

ng cc nhu cu khc nhau nh Dragon cho lnh vc y khoa, Dragon phc v hc

tpTuy nhin v y l mt chng trnh m ng nn khng c kh nng

nghin cu. Chi tit tham kho ti http://www.nuance.com/dragon/index.htm.

Trong nc:

Mc d th gii c nhiu cng trnh nghin cu v ng dng mang li thnh

cng nh vy, nhng do nhiu l do m trong nc cha c mt h nhn dng

ting ni no c pht trin mt cch hon chnh cng nh rt ti nghin

cu v lnh vc ny. c bit n nhiu nht trong nhn dng ting Vit l

chng trnh Vspeech ca nhm sinh vin ti trng i hc Bch khoa TpHCM.

y l chng trnh ot gii thng Tr tu Vit Nam nm 2004. Vspeech l


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mt chng trnh hot ng da trn b my nhn dng ting ni ca Microsoft

tch hp sn trong Windows.

Cch hot ng ca Vspeech ht sc n gin, da trn s tng i ging

nhau khi phin m latin ca mt s t ting Anh v ting Vit, nhm Vspeech s dng chng trnh nhn dng ting ni ca Microsoft cung cp, thc hin thao

tc nhn dng sau nh x t ting Anh nhn c sang t ting Vit c phin

m latin gn ging nht.

V d, thai trong ting Vit pht m gn ging vi hi- ngha l xin cho-

trong ting Anh. Khi mt ngi ni hai, b nhn ging ting ni ca Microsoft

s cho kt qu l hi, t kt qu ny, Vspeech s nh xhi vi hai trong

ting Vit v cung cp kt qu cui cng ca thao tc nhn dng l hai, ng vitm ngi ni mong mun.

Vi cch lm ny, cng vic ch yu ca nhm Vspeech l tm ra nhng t

ting Anh c phin m gn ging vi t ting Vit, sau ch cho php b nhn

dng ting ni (ting Anh) ca Microsoft chp nhn cc t ny l kt qu nhn

dng cui cng. B t vng ny sc nh x vi mt b t ting Vit cng

phin m tng ng. Vic cn li l t kt qu l t ting Anh c c t b nhn

dng ca Microsoft, Vspeech s nh x sang t ting Vit tng ng v a ra ktqu nhn dng l t ting Vit ny.

u im trong cch lm ny l khng cn phi xy dng mt b nhn dng

ting ni m s dng li ci c sn, thi gian xy dng ng dng nhanh.

Tuy nhin, cch lm ny l khng bn vng v:

- Khng phi t ting Vit no cng c t ting Anh pht m gn ging.

- Nhng t ting Vit ch khc du pht m gn ging nhau s kh phn

bit trong qu trnh nhn dng.

- Khng nhn dng c khi ni nhiu t lin tc.

Nhng nhc im trn l bi v b nhn dng ting ni ca Microsoft l mt

b nhn dng ting ni dnh cho ting Anh v mt s ngn ng khc m khng h

trting Vit, trong khi c im v ng m, ng php, m hnh ngn ng ca cc


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ngn ngkhc nhau l khc nhau. Do m chnh xc khi nhn dng l khng

cao cng nh khnng p ng thp.

V l do ny m nhm thc hin ti nghin cu chi tit v cc k thut s

dng trong nhn dng ting ni ni chung v cc h nhn dng cc ngn ng khcc mm ngun, tng bc xy dng mt h nhn dng ting ni dnh cho

ting Vit.


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CHNG2

CSLTHUYT

Chng ny strnh by s qua vcc vn l thuyt c bn v quan trng

c sdng khi xy dng mt h nhn dng ting ni trong chng ti.

2.1.L THUYT NGM2.1.1.L thuyt v ting niMc ch ca ting ni l truyn thng tin. C mt s c trng cho vic

truyn ting ni. Theo l thuyt thng tin, ting ni c th biu din di dng ni

dung thng bo hoc thng tin. Mt cch c trng khc l ting ni biu din

di dng tn hiu mang thng tin thng bo. Mc d cc quan im l thuyt ca

thng tin ng vai tr cho trong cc h thng truyn tin phc tp, ta s thy l

biu din ting ni da trn dng sng hoc m hnh tham sc s dng chnh

trong cc ng dng thc t.

xt qu trnh thng tin ting ni, u tin nn coi thng bo nh mt dng

tru tng no trong u ngi ni. Qua qu trnh phc tp to m, thng tin

trong thng bo ny c chuyn trc tip thnh tn hiu m hc. Thng tin thng

bo c thc biu din di mt s dng khc nhau trong qu trnh to tingni. Chng hn, thng tin thng bo lc u c chuyn thnh tp hp cc tn

hiu thn kinh iu khin c chpht m ( l chuyn ng ca li, mi, dy

thanh m). B my pht m chuyn ng tng ng vi cc tn hiu thn kinh

ny to ra dy cc iu b, m kt qu cui cng l dng sng m cha thng

tin trong thng bo gc.

Thng tin c thng bo bng ting ni v bn cht l ri rc, c th biu

din bi vic dn cc phn tmt tp hp hu hn cc k hiu. Cc k hiu mmi m c thc phn loi ra gi l cc m v (phoneme). Mi ngn ng c tp

hp cc m v ring ca n, con s mu mc l khong t30 n 50. V d ting

Anh c th biu din bng khong 42 m v, ting Vit khong 33 m v ( 12

nguyn m : a, , , o, u v 21 phm: k, l, m, ph ).


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Trong l thuyt thng tin ngi ta cn xt tc truyn thng tin. Vi ting

ni, lu n cc gii hn vt l ca tc chuyn ng ca b my pht m,

nh gi th ca tc thng tin l con ngi to ra ting ni vi tc trung

bnh khong 10 m v trong 1 giy. Nu mi m v biu din bng mt s nh phnth m s6 bit l qu biu din tt c cc m v ting Anh. Vi tc trung

bnh khong 10 m v trn giy v bqua tng tc gia cp m v lin k, ta c

c lng 60 bit/giy cho tc thng tin trung bnh ca ting ni. Ni cch khc

l lng vit ra ca ting ni cha thng tin tng ng vi 60 bit/giy tc

ni chun. D nhin, cn di ca ni dung thng tin xc thc trong ting ni c

coi l cao hn tc ny. c lng trn khng tn n cc nhn tnh trng thi

ca ngi ni, tc ni, m hng ca ting ni,v. v2.1.2. Mt sc im ngm ting VitMt c im d thy l ting Vit l ngn ngn m (monosyllable - mi t

n ch c mt m tit), khng bin hnh (cch c, cch ghi m khng thay i

trong bt c tnh hung ng php no). Ting Vit hon ton khc vi cc ngn

ngn-u nh ting Anh, ting Php l cc ngn nga m, bin hnh.

Nhn v mt ghi m: m tit ting Vit c cu to chung l: ph m-vn. V dm tin c ph m t, vn in. Ph m l mt m v v m v ny lin kt rt lng lo

vi phn cn li ca m tit (hin tng ni li).

Vn trong ting Vit li c cu to t cc m v nhhn, trong c mt

m v chnh l nguyn m.

Hnh sau l ph tn hiu ca m tit ba. Chng ta c th quan st v phn bit

r min nhiu nn, min ph ca ph m b v nguyn m a (min m hn l cmt nng lng ln hn).


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Hnh 2.1: Ph tn hiu ca m tit ba, c min nhiu nn (silence), min tn hiu ca ph m

/b/ v nguyn m /a/ (min m hn l c mt nng lng ln hn).

Quan st ph cc m tit tng t chng ta c th rt ra kt lun: cc ph m

v nguyn m u phn bit vi nhau rt r qua s phn bnng lng ti cc

min tn s, v d: ph m tn s thp, nng lng nh, nguyn m c nng

lng ln c vng tn s cao. Vng khng c tn hiu ting ni (nhiu nn v

khong lng) c nng lng thp v ch tp trung cc tn s rt thp.

Cc nguyn m c tn ph (spectrum) khc nhau kh r. Hnh sau minh ho s

khc nhau v ph ca 5 nguyn m c bn. Min m l min c mt nng

lng cao.


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Hnh 2.2: S khc nhau v ph ca 5 nguyn m c bn. Min m l min

c mt nng lng cao (vng c formant).

Theo tc gion Thin Thut , xt v mt ng m-m v hc m tit ting

Vit c lc nh sau:

Thanh iu

m u Vnm m m chnh m cui

Lc cho thy m tit ting Vit c cu trc r rng, n nh. Lc cn

cho thy ting Vit l ngn ngc thanh iu. H thng thanh iu gm 6 thanh:

bng, huyn, sc, hi, ng, nng.

Thanh iu trong m tit l m vsiu on tnh (th hin trn ton b m tit).Do c trng vthanh iu th hin trong tn hiu ting ni khng r nt nh

cc thnh phn khc ca m tit.


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S khc bit v cch pht m ting Vit rt r rt theo gii, la tui v c bit

l theo v tr a l (ging min Bc, min Trung v min Nam khc nhau rt

nhiu).

2.1.3. L thuyt v m v2.1.3.1. nh ngha m v

C nhiu cch nh ngha m v khc nhau:

Theo cun Ng m hc ting Vit hin i, NXBGD 1972, nhm tc gi C

nh T th m vl n v nh nht ca ngm c mang chc nng phn bit

ngha v nhn din t.

Theo cun ng m ting Vit ca on Thin Thut th m vl tng thcc

nt khu bit, c xut hin ng thi (c con ngi tri gic theo trt ttrc

sau) v c chc nng khu bit v m thanh ca thoc hnh v.

Theo Gio s Cao Xun Ho, nhng cch nh ngha trn cn c nhng ch

cha tha ng: mang tnh cht n tng chngha, c s lm ln v cch tri gic

tnh ng thi, k tip v theo ng th m v l n v khu bit m thanh nh

nht c ththam gia vo thi lp m v hc vtrt tthi gian, hoc m v l

n v m v hc tuyn tnh nh nht.

Theo inh L Th v Nguyn Vn Hu, ngi ta thng nh ngha m v l

n v nh nht ca c cu m thanh ngn ng, dng cu to v phn bit hnh

thc ngm ca nhng n vc ngha ca ngn ngtv hnh v. V d: cc t

ti v i, ta v a trong ting Vit phn bit nhau bi cc m v/t/ v //. Nu

thay m v ny bng mt m v khc trong cng mt m tit slm cho m tit thay i vngha hoc mt ngha. V d, ta c tton, nu thay m v /t/ bng

m v /h/, th sc hon c ngha khc.


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2.1.3.2.Chc nng ca m vCc m v trn nguyn tc nht nh phi c s khc nhau, t nht l v mt c

trng no . Chnh nhs khc bit ny m cc m v c th to ra s khc bit

v hnh thc m thanh ca hnh v v t, to nn nhng tn hiu khc bit i vis cm th ca con ngi. Theo , m v c 2 chc nng c bn: chc nng khu

bit v m thanh ca hnh v v t, v chc nng cu to nn nhng thnh t ca

n vc ngha.

2.1.3.3. Tch m vv xc nh m v trn chui sng mSlng t trong mi ngn ngu rt ln. Xy dng h nhn dng theo t c

khnng phn bit s lng t qu l mt thch thc. Thay vo , ngi ta

ngh ra cch xy dng h nhn dng da trn hng tip cn m v. Theo , chcn nhn dng khong vi chc m v s c th nhn dng c ton b t ca mt

ngn ng (Theo thng k, s m v trong mt ngn ngdao ng t khong 20

n 60). V y cng chnh l hng tip cn ng n cho nhn dng ting ni

ting Vit. Tuy nhin, ngi ta li gp kh khn khc, l tch m vv xc nh

m v trn chui sng m: Cho mt dy tn hiu ting ni thu sn. Nhim v

ca chng ta l tm ranh gii ca tt c cc m v v cho bit m v l m v g.

Cha ni n khnng thc hin cng vic bng my, ngay ccon ngi vnc th b nhm ln khi tch m v bng tay do ranh gii gia cc m v thng

mp mv hay chng lp ln nhau. C khi 2 m v thuc 2 m tit khc nhau, nu

ng k nhau vn c th xy ra s chng lp. V vy, cng vic tch m v trn

chui sng m chmang tnh tng i.

Nhng thun li v kh khn i vi nhn dng ting ni ting Vit

Thun li

Nhng c im ng m ting Vit cho thy nhn dng ting ni ting Vit c

mt s thun li sau:


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Ting Vit l ngn ngn m, slng m tit khng qu ln. iu ny

s gip h nhn dng xc nh ranh gii cc m tit ddng hn nhiu. i vi h

nhn dng cc ngn ngn-u (ting Anh, ting Php...) xc nh ranh gii m

tit (endpoint detection) l vn rt kh v nh hng ln n kt qu nhndng.

Ting Vit l ngn ng khng bin hnh t. m tit ting Vit n nh, c

cu trc r rng. c bit khng c 2 m tit no c ging nhau m vit khc

nhau. iu ny s d dng cho vic xy dng cc m hnh m tit trong nhn

dng; ng thi vic chuyn t phin m sang t vng (lexical decoding) sn

gin hn so vi cc ngn ngn-u. Vic chuyn t phin m sang t vng cng

l mt vn kh khn trong nhn dng cc ngn ngn-u.

Kh khn

Ngoi nhng thun li trn, nhn dng ting ni ting Vit cng gp rt nhiu

kh khn nh sau:

Ting Vit l ngn ng c thanh iu (6 thanh). Thanh iu l m v siu

on tnh, c trng vthanh iu th hin trong tn hiu ting ni khng r nt

nh cc thnh phn khc ca m tit.

Cch pht m ting Vit thay i nhiu theo vtr a l. Ging a phng

trong ting Vit rt a dng (mi min c mt ging c trng).

H thng ng php, ngngha ting Vit rt phc tp, rt kh p dng

vo h nhn dng vi mc ch tng hiu nng nhn dng. H thng phin m

cng cha thng nht.

Cc nghin cu v nhn dng ting Vit cng cha nhiu v t ph bin.

c bit kh khn ln nht l hin nay cha c mt b d liu chun cho vic

hun luyn v kim tra cc h thng nhn dng ting Vit.

2.2.L thuyt xl tn hiu s


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Trong cc h thng truyn ting ni, tn hiu ting ni c truyn i, lu gi

v x l bng nhiu cch. Cc gii php k thut cho ta nhiu cch biu din tn

hiu ting ni. C 2 cch chnh:

-

Lu gi ni dung thng bo trong tn hiu ting ni.- Biu din tn hiu ting ni di dng thun tin truyn i hc lu gi,

hoc di dng linh ng c th sa cha m khng nh hng n ni dung

thng bo.

Biu din tn hiu ting ni phi lm sao cho ni dung thng tin c th d

dng lnh hi c bi ngi nghe hoc bng my tng. Trong vic thit k v

x l cc biu din ny, cc phng php x l tn hiu ng vai tr c bn.

2.2.1 Xl tn hiuTrong trng hp tnh hiu ting ni, ngi ta coi ngun thng tin, o c

hoc quan st, ni chung, l c dng sng m. X l tn hiu bao gm trc ht l

nhn c biu din tn hiu da trn m hnh cho v sau l dng bin i

mc cao hn t tn hiu v dng tin dng hn. Cc thao tc v x l thng tin

c vnh hnh di y.

Bc cui cng ca x l tn hiu l trch ra v s dng thng tin. Bc ny c

thc thc thc hin hoc bi ngi nghe hoc tng bng my. Ly v d l


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h thng c chc nng nhn bit tng ngi ni t mt tp hp ngi cho,

c th s dng biu din ph ph thuc thi gian ca tn hiu ting ni. Mt bit

i tn hiu c th dng l ph trung bnh mt cu y , so snh ph trung

bnh vi phtrung bnh lu tr ca mi ngi ni, ri sau da trn sotng t ca ph m nhn bit ngi ni. v d ny, thng tin trong tn hiu

dng nhn dng ngi ni. Thao tc tnh ton so tng t, tm cu ph hp

nht vi tn hiu ting ni lin quan n n tnh ton xc sut v thng k

c trnh by phn tip theo ca chng.

2.2.2Xl tn hiu sX l tn hiu s tp trung vo 2 vic chnh l nhn c cc biu din ri rc

ca tn hiu v l thuyt, thit k, thc hin cc th tc s x l cc biu din

ri rc ny. i tng ca x l tn hiu s l nhn bit cc i tng trong x l

tn hiu tng t. Cu hi t ra l v sao cc k thut x l tn hiu s li c

dng nghin cu thng tin ting ni? u tin v quan trng nht l cc hm x

l tn hiu phc tp c th thc hin bng cch dng k thut s. Khi x l tn hiu

ting ni, nhiu trng hp khng th coi cc h thng ny l cc h thng xp x

ca cc h thng tng t.

Cc k thut x l tn hiu slc u c dng trong cc h thng x l ting

ni nh m phng cc h thng tng t phc tp. Quan im lc u l phi m

phng cc h thng tng ttrn my tnh trnh vic xy dng cc h thng

thc nghim. Xc tc chnh l s pht trin ca my tnh nhanh hn v cc tin b

nhanh trong l thuyt k thut x l tn hiu s. Nh vy, cc h thng x l tn

hiu s c khnng m phng cc htng t tt, cng thm vi cc pht trin v

l thuyt v phn cng slm tng u th ca cc h thng x l tn hiu s so vicc h thng tng t. Cc h thng s trnn ng tin cy v rt cht ch.

Cng ngh cho php cc h thng cc k phc tp c th hot ng trn mt

chip n, cc thnh phn logic nhanh s ln cc tnh ton thc t trong


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nhiu hm x l tn hiu c th thc hin trong thi gian thc v tc mu

ting ni.

C nhiu l do khc dng k thut s trong cc h thng thng tin ting ni.

Chng hn, nu m ha c dng, ting ni di dng s ha c th truyn imt cch tin cy trn cc knh rt n. Cng vy, nu tn hiu ting ni dng s

th n ng nht vi d liu ca cc dng khc. Do vy, mt h thng c th dng

truyn tn hiu ting ni cng cc tn hiu khc m khng cn phn bit chng

tr vic gii m. Ngoi ra, v yu cu bo mt vic truyn tn hiu ting ni, biu

din sc u thhn hn so vi cc h thng tng t. Vi cc l do trn v

nhiu l do khc na m cc k thut sc s dng ngy cng nhiu trong cc

bi ton v ting ni.2.2.3C sxl tn hiu sTrong hu ht tnh hung x l hoc truyn thng tin, ngi ta phi bt u

bng vic biu din tn hiu nh mu bin i lin tc. Sng m pht ra cng c

bn cht nh vy. V mt ton hc, c th biu din cc mu bin i lin tc nh

vy l hm ca bin lin tc tbiu din thi gian. Trong phn l thuyt ny, k

hiu x(t) cho dng sng thi gian bin i lin tc. Cng c th biu din tn hiu

ting ni nh cc dy s, k hiu x(n) dng biu din dy s.Khi nghin cu v cc h thng x l tn hiu ting ni ngi ta s s dng

mt s dy sc bn nh dy xung n v, dy bc n v, dy ly tha


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X l tn hiu i hi bin i tn hiu thnh dng mong mun theo mt ngha

no . Lp cc h thng bt bin dch chuyn tuyn tnh (LSI Linear Shift

Invariant) thng c dng trong x l ting ni. Cc h thng ny c c

trng hon ton bi p ng ca chng vi u vo. Vi cc h thng ny, u ray(n) c t tnh c tu vo x(n) v p ng ca mu n v h(n) theo tch

chp:

y * l k hiu tch chp ri rc (discrete convolution). Biu thc tng

ng l:

Cc h thng LSI thng dng lp cc php lc trn cc tn hiu ting ni

v c bit l trong cc m hnh to ra ting ni.

Khi c c cch biu din ting ni dng s, ngi ta tin hnh cc thao

tc x l tn hiu bng cc php bin i nh bin i Z (Z TransformZT), bin

i Fourier (Fourier Transform FT), bin i Fourier ri rc (Discrete FT DFT) L thuyt v x l tn hiu s c th tm thy cc gio trnh mn X l

tn hiu s.

CHNG 3


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M HNH HMM V NHN DNG TING NI

3.1.Gii thiuTrong phn ny cc phn c bn ca m hnh HMM sc gii thiu. Cc

nh ngha, cc tp hp tham s, cc vn thit yu, cc thut ton chnh ca mhnh HMM p dng vo nhn dng ting ni sc gii thiu. Tip cc phn

chnh ca h nhn dng, cc cng on chnh ca nhn dng da vo m hnh

HMM cng sc gii thiu s qua

3.2.Nhng vn c bn ca HMMM hnh HMM l m hnh thng k thng xuyn c s dng m hnh

ha ting ni, s dng cho cng vic nhn dng. Cu trc bn trong ca HMM

khng phi da vo kin thc v ting ni nhng n li c s dng trong nhndng tnh ton cc c trng s ca ting ni.

3.3.Cc kin thc ton hc ca HMM v cc vn khi sdng HMM vonhn dng ting ni

M hnh Markov n HMM l mt m hnh thng k da vo m hnh Markov.

V vy hiu c m hnh HMM chng ta s xem xt qua v m hnh Markov

v m hnh thng k ni chung.

3.3.1.Gii thiu v nhn dng thng k v HMMQu trnh thng k l qu trnh xc nh xc sut ca mt s s kin v xc

sut mi quan h gia cc s kin trong mt tin trnh ti cc thi im khc nhau.

Bin cngu nhin v hm mt xc sut

Gi X l tp cc bin ngu nhin , X = {X1,X2, , Xn} m tn ti t nht mt

s kin ca tp X ny xut hin. Gi xc sut ca s kin Xi l P(Xi). Khi ta cxc sut ca X l P(X) = 1. Nu gi P(Xi) l xc sut ca bin c Xi th ta c:

1iP X P X (3.1)


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Xc sut c iu kin:

Gi A v B l cc bin ngu nhin. Xc sut c iu kin c m tnh

sau:

Gi s s kin A xy ra vi xc sut P(A). Xc sut ca s kin A vi

iu kin s kin B xy k hiu l P(A|B) c tnh nh sau:

Trong nhn dng thng k, hai hm xc sut c iu kin sau thng c

dng:

- P(x|Ci): hm mt xc sut ca o vector x thuc v lp Ci, vi

gi thit l xc sut P(Ci) c bit trc hay c thc lng c.

- P(Ci|x): vi iu kin x xy ra, xc nh xc sut xut hin ca lp ri

rc Ci(cha bit), thng qua P(C

i): xc sut ca lp C

iv P(x|C

i).

Mt tin trnh c gi l tin trnh Markov ( Markov process) nu xc sut

ca mt s kin ti mt thi im b rng buc bi cc s kin trong qu kh xc

nh. Nh vy, m hnh Markov l mt m hnh thng k thun ty. Trng thi l

mt nh ngha gip chng ta hiu c s bin i ca s kin theo thi gian.

Bin c chnh trong tin trnh Markov l t trng thi i ti thi im t. Mt

tin trnh Markov c s dng trong cc h thng nhn dng ting ni tng

(ASR) tun theo cc iu kin sau:

1. Ch tn ti mt thi im phn bit trong chui thi gian t = 1,2,, T;

2. Ch c mt slng trng thi xc nh {st} ={i}, i = 1,2,,n;

( )( | ) ( ) 0

( )

P ABP A B P B

P B (3.2)


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3. Trng thi hin ti v qu kh ch l cch nhau mt bc:

Nhim v chnh ca tin trnh Markov l to ra chui trng thi S=s1,s2,...,sT.

M hnh Markov n HMM c pht trin da trn m hnh Markov. Cc kha

cnh chnh yu v s dng m hnh HMM trong nhn dng ting ni sc trnh

by di y.

3.3.2.Cc thnh phn chnh ca HMMThnh phn chnh ca HMM gm tp hp trng thi v cc tp hp tham s

chnh.

Hnh 3.1 M hnh HMM 6 trng thi

Tp hp cc trng thi v ba tp hp cc tham sxc nh 1 m hnh HMM.

N c trng cho mt tin trnh khng bit trc th tc m tnh trong

[Hnh 3.1].

1 2 1| , ,..., |t t t t k t t P s s s s P s s (3.3)


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u tin S={si, i = 1,, n} (vi n l s trng thi ca HMM) l tp hp

cc trng thi ca m hnh HMM.

Tp hp tham s th nht c gi l xc sut chuyn trng thi

(transition probabilities) c nh ngha nh sau:

Tp hp cc xc sut khi to m hnh HMM i: ={i}.

Tuy nhin trong nhn dng ting ni cc m hnh HMM ch yu c khi

to ti trng thi u tin nn ta b qua tp xc sut khi to m hnh HMM.

ngha ca aij l: xc sut chuyn trng thi t trng thi i ti thi im t-1

sang trng thi j ti thi im t. Chng ta gi ma trn A = {aij} l ma trn chuyn

trng thi.i vi m hnh Markov, khi trng thi trc c xc nh th xc

sut chuyn trng thi ti trng thi tip theo cng hon ton xc nh.

p dng HMM vo cc sng m thanh, mt hm thng k sc gn

vo cc trng thi. u tin sng m ting ni sc chuyn i thnh chui cc

vector c trng theo thi gian (sc gii thiu trong phn rt trch c trng

sng m). Chui cc vector c trng ny gi l chui cc vector quan st

O=o1,o2 ,, oT, vi ot l vector c trng cho chui sng m ti t. Xc sut m

hm thng k ni trn tnh l xc sut vector c trng ot t trng thi j ti thi

im t. Xc sut ny gi l xc sut quan st hay xc sut output v n c trng

cho tp tham s th 2 ca HMM:

t B={bj(ot)}.

ij 1|t ta P s j s i (3.4)

| ( 1, 2,..., ; 1, 2,..., ) j t j t b o P o s j t T j n (3.5)


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Tng qut m hnh HMM c th khi to ti bt k trng thi no, xc sut

m hnh HMM khi to ti trng thi i k hiu l i. Tp xc sut ={i}, gi l

tp xc sut khi to m hnh HMM, l tp trng thi th 3 ca m hnh HMM.

Tuy nhin trong bi ton nhn dng ting ni, hu ht cc m hnh HMM u khito ti trng thi u tin nn chng ta khng cn ti tp xc sut th 3 ny.

Nh vy trong nhn dng ting ni mt m hnh HMM sc c trng

bi tp trng thi v 2 tp tham s A v B ni trn: = (A,B).

3.3.3.V d v nhn dng tn da trn HMMGi s chui sng m ca t cn nhn dng c m ha bi chui vector

c trng (chui quan st) O=o1,o2,,oT vi oil vector c trng ti thi im t.Vic nhn dng ting n l i tnh:

C ngha l tm t c xc sut P(wi|O) ln nht, vi wi l t(i vi ting

Vit l m tit) trong danh sch t cn nhn dng (tng qut l t trong tin),

trong nhn dng tny c m hnh ha bi mt s m hnh HMM. Xc sut

ny khng thtnh c trc tip nhng c thdng nh lut Bayes:

y xc sut P(O) l hng s khi cho O trn tt c cc t c th wi. Xc

sut P(wi) ch lin quan n m hnh ngn ng (s gii thiu trong phn sau),chng ta cng c thxem nh l hng s. Nh vy vn ca vic nhn dng ch

l vic tnh xc sut P(O|wi).

arg ax w |im P O (3.6)

| w ww |

i i

i

P O PP O

P O (3.7)


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V d, trong mt m hnh nhn dng n gin nht, mi m tit wi sc

m hnh ha bi m hnh HMM i, nh vy vic tnh xc sut P(O|wi) c th qui

v tnh xc sut P(O|i).

Trong trng hp nhn dng m v mi m tit wi khng tng ng vi mt

m hnh i. Mi m tit tng ng vi mt dy cc m v, mi m vc m

hnh ha bi mt m hnh HMM nn mi m tit c m hnh ha bi dy cc

HMM m v1, 2, ,k. V vy vic tnh xc sut P(O|wi) c qui v tnh xc

sut P(O| 12k).

3.3.4.Hai gi thuyt c bn xy dng h thng nhn dng da trnHMM

Gi thuyt 1: gi thuyt v xc sut chuyn trng thi:

Gi thit th nht da trn chnh m hnh Markov. V xc sut chuyn trng

thi aij ch ph thuc vo trng thi pha trc n, khng h ph thuc vo chui

quan st nn ta c th xem aijnh l hng. Xc sut chuyn trng thi xut hin ti

cc thi im khc nhau v cc trng thi khc nhau nn ta c th xem chng l

c lp. V vy vic tnh xc sut ca mt chui trng thi wi trong mt m hnh

HMM tng t c th qui v:

Gi thuyt 2: Gi thuyt v xc sut quan st:

Gi chui trng thi ca m hnh HMM ng vi chui vector quan st O l

chui quan st. Gi vic tm chui trng thi trong m hnh HMM c xc sut cao

nht ng vi 1 chui quan st O gi l quan st O. Tnh ngha ca xc sut

quan st b chng ta c th thy rng xc nh chui quan st O (xc nh chui

trng thi ng vi chui vector c trng O) cng l mt tin trnh thng k. Tuy

nhin n khng phi l chui Markov. Khi mt HMM tin hnh m hnh ha mt

1 ( 1) ( )| |T T

t t s t s t

i i

P S P s s a (3.8)


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chui quan st ca ting ni (tc xc nh chui quan st ng vi chui vector c

trng sng m), mi trng thi c th pht sinh ti bt k vector quan st no (vi

mt s rng buc), nhng vi xc sut khc nhau. Do s khng bit c trng

thi no s gn vi vector no. Nh vy s khng bit c chui trng thiS=s0s1...sT no s pht sinh ti chui vector c trng O cho trc. y chnh l

iu tin trnh Markov ny c gi l n. Mc d xc sut ca s kin quan st

vector ot(xc nh trng thi ca Ot) ti cc thi im t khc nhau l c lp v

hon ton xc nh c (iu ny l rt cn thit i vi tt c cc qu trnh tnh

ton da trn HMM).

V vy nn gi thit th 2 l:

Cho tp hp trng thi S ca m hnh HMM , ta c:

Vi bst(Ot) l xc sut ca vector c trng Ot t trng thi s ti thi im t.

Vi P(S|) v P(O|) c tnh ton theo 2 gi thit trn ta c th tnh xcsut kt ca O v S c to ra bi m hnh nh sau:

Tuy nhin trong thc t chui trng thi S li khng bit, v vy tnh

P(O|) phi tnh tng trn cc chui S c th c:

1

| ,t

T

s t

t

PP O S b O

(3.9)

, | | | ,P O S P S P O S (3.10)

(3.11) | | | ,S

P O P S P O S


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V vy ta c:

Trong mt s ti liu c thm xc sut nhng HMM lun khi to t trng

thi u tin nn c th b qua xc sut khi to .

Theo cng thc trn, vi s trng thi ca HMM l N th xc sut ny c n

2*T*NT php nhn. Thm ch vi N=5 v T=100, cng thc trn cha xp x 1070

php nhn. phc tp ny qu ln v vy cn c thut ton hiu quhn xc

nh P(O|).

3.3.5.Ba vn thit yu ca HMM v cc cch gii quytGi s cho mt HMMs =(A, B) v chui quan st O= O1, O2,, On

Tt c cc ng dng da trn m hnh Markov n s phi gii quyt 3 vn

c bn sau:

i.Vn tnh ton: Lm sao tnh c P(O|) (xc sut ca

vic xut hin chui quan st O trong m hnh HMMs) vi khi lng tnh

ton ti thiu.

ii.Vn c lng tham scho HMM: Vn ny c t ra

trong qu trnh hun luyn. Chng ta sxc nh c cc m hnh da

1 1 2 2 11 2

| | , |

...T T T

S

s s s s s s s T

s

P O P O S P S

b O a b O a b O

(3.14

(3.12)

(3.13)

1 21 2

| , ...TS S S T

P O S b O b O b O

1 2 2 3 1

| ...T T

S S S S S SP S a a a


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vo d liu hun luyn. Lm sao xc nh c cc tham s ca m hnh

HMM =(A,B) sao cho P(O|S,) (hoc P(O,S|) l ln nht.

iii.Vn Decoding(nhn dng): Cho mt m hnh HMM

c hun luyn. Lm sao tnh c chui trng thi S= s1, s2,, sT tng

ng vi chui quan st O P(O,S|), sao choxc sut ca chui trng thi

ca chui quan st O trng vi chui S l ln nht.

Trc khi nu cch gii quyt 3 vn trn xin trnh by 2 thut ton c lin

quan l gii thut forward-backward.

Gii thut Forward

Hm forward t(i) c nh ngha nh sau:

Vi t(i) l xc sut kt ca vic quan st t vector sng m u tin t

trng thi i ti thi im t.

t(i) c thc tnh qui nh sau:

1. t(i) = ibi(O1), 1iN (N l s trng thi s)

2. vi t = 1,2, ,T-1, 1N

Nh vy c thtnh c xc sut:

1 2, ,..., , |t t ti P O O O s i (3.15)

1 ij 1

1

( ) ( ) ( )N

t t j t

i

j i a b O

3.16

1

| ( )N

T

i

P O i

(3.17)


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Gii thut Backward

Hm backward t(i) c nh ngha nh sau:

ngha ca hm ny nh sau: n l xc sut kt ca chui vector sng m

thi+1 n vector sng m th T vi trng thi i ti vector tht v m hnh . N

khc trng hp gii thut forward l trng thi ti vector c trng th t (l trng

thi i) l bit trc.

C th tnht(i)qui nh sau:

1. Vi t = T:

t(i) = 1 1 i N

2. Vi t = T-1, T-2, , 1 ta c

Nh vy ta c:

3.3.5.1.Gii quyt vn tnh tonVn ny c gii quyt bng thut gi Forward. p dng thut gii

Forward, chng ta ch mt N2T, so vi 2T*NT ca phng php tnh trc tip. V

d vi trng hp N=5 v T=100 th my tnh ch phi thc hin khong 3000

php nhn thay v 1070 php nhn nh ca phng php trc tip.

ij 1

1( ) ( ) ( )

N

t j t t

ji a b O i

(3.19)

1 2( ) ( , ,..., | , )t t t T t i P O O O s i (3.18)

1 11

| ( ) ( )N

i i

i

P O b O i

(3.20)


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3.3.5.2.Gii quyt vn c lng tham s cho HMMC 2 gii thut gii quyt vn ny l gii thut phn on K-mean v

gii thut Baum-Welch.

Gii thut c lng tham sBaum-Welch: y tham s ca m hnh

=(A,B) c tnh ton nhm tng xc sut P(O|) cho n khi n t gi tr cc

i. Nh trnh by trn vic tnh ton P(O|) l tnh tng tt ccc P(O,I|)

trn tt c cc chui trng thi I ch khng phi cho mt chui ring bit no.

Phn quan trng ca thut ton Baum-Welch l hm expectation-

maximisation (EM). Thut ton ny c s dng gii quyt tnh trng thngtin khng y trong d liu hun luyn (tc khng bit c chui trng thi).

Hm EM thng c s dng nht trong nhn dng ting ni l chun

maximum-likelihood (ML). Gii php ca gii thut ML l a ra cc cng thc

nhm cp nht cc gi tr tham sc ca HMM. qu trnh hun luyn t c

cc tham s tt th cn c cc tp tham s khi to ca HMM tt, bi v Baum-

Welch l mt thut ton ch cho kt qu tt nht trong cc b.

tng ca ML l c lng cc tham s ca HMM sao cho xc sut

likelihood P(O|) ln nht vi tp hp cc chui quan st {O}. Mt im na ca

ML l thut gii khng thc hin tinh P(O|) trn tt c cc chui quan st m ch

mt s chui S c P(|S) vt tri. iu ny lm gim chi ph tnh ton rt nhiu

nhng kt qut c khng gim bao nhiu. Trong thc t thun tin cho

tnh ton ngi ta khng dng likelihood nguyn thy m dng xc sut

log_likelihood(ly logarit ca likelihood).

Trong thc tc lng cc tham s ca HMM ngi ta t s dng thut

ton Baum-Welch nguyn thy v chi ph tnh ton ca n qu ln. Thay vo

thut ton Baum-Welch c tnh da vo thut ton Forward v Backward. V

vy chng ta thng nhm thut ton Baum-Welch v thut ton Forward-

Backward.

1

| ( )N

T

i

P O i

(3.21)


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3.3.5.3.Gii quyt vn decodingVn ny c gii quyt bng gii thut Viterbi.

Gii thut ny tm ra chui S= s1, s2,, sT sao cho s xut hin chui vector

c trng O = O1, O2,, OT trong chui trng thi I l ln nht. C ngha l phi

tm chui trng thi S sao cho P(O,S|) l ln nht. y l mt gii thut qui np

v n c s dng trong qu trnh nhn dng sau khi qu trnh hun luyn tm

ra c cc m hnh HMM. Gii thut Viterbi trnh c tm kim trn khng

gian trng thi ln ca m hnh HMM nn gim thiu c chi ph tnh ton.

nh ngha thm:

Suy ra:

V vy bi ton tm chui trng thi tt c xc sut cao nht:

Tng ng vi bi ton tm:

1 1 2 2 11 2

| | , |

...T T TS S S S S S S T

P O P O S P S

b O a b O a b O

(3.22)

1 11 2 1

2

, ,..., ln lnT T tT s s S S t

t

U s s s b O a b O

(3.23)

1 2( | ) exp( ( , ,..., ))TP O U s s s (3.24)

1{ } 1

ax ( , ... | )T Ts t

m P O s s (3.25)

1 2{ } 1

min ( , ,..., )T

T

Ts t

U s s s

(3.26)


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C th xem ln( ( )) j k t i i s t

a b O l hm chi ph khi i t trng thi sj sang

trng thi sk ti thi im t (ti vector c trng th t).

Thut ton Viterbi c thc m tnh sau:

Gi schng ta ang vector c trng thttrong chui vector c trng v

ang trng thi i trong m hnh HMM, chng ta mun chuyn qua trng thij

trong m hnh HMM. Chi ph chuyn t trng thi i sang trng thij l trng

sln(aijbj(Ot)) (vi aijbj(Ot) l xc sut chuyn t trng thi i sang trng thij ti

thi im tv vector c trng Ott trng thij) vi Ot l vector c trng c

chn trong chui O=O1,O2,,OT khi chuyn ti trng thi j. Ti thi im t=1

trng s ny lln(bi(O1)), trng sny c gi l trng s khi u. Nh vy

tng trng s ca chui trng thi s l tng cc trng s chuyn trng thi gia 2

trng thi knhau. Nh vy bi ton tm chui trng thi c xc sut cao nht s

tng ng vi bi ton tm chui trng thi c tng trng nh nht.

3.4.Nhn dng ting ni v nhn dng m v da trn HMM3.4.1.M hnh nhn dng

Bt kchng trnh nhn dng da trn HMM no cng phi tun t triqua 2 giai on pht trin, u tin l giai on hun luyn v sau l giai on

nhn dng

Giai on hun luyn:

Trong giai on ny, d liu sng m ting ni c trch xut cc thng s

c trng, gn nhn m v v kt qu cui cng l cc m hnh HMM ca cc

m v. y l giai on quyt nh i vi chnh xc khi nhn dng ting ni.

Cc thao tc thc hin trong giai on ny nh Hnh 3.3.1.


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Giai on nhn dng:

Trong giai on hun luyn chng ta s dng thut ton Baum-Welch

c lng tham s cho HMM. Vic hun luyn thc hin trn d liu gn nhn

hoc khng gn nhn.

D liu ting ni c gn nhn theo m v l d liu m trn cxc nh bin ca m v ca tng t trn chui sng m. Cc nhn ny c gn

bng tay. Cn d liu khng gn nhn c nhiu mc . Trong bi lm th d liu

khng gn nhn c hiu theo ngha l chxc nh chui m tit (tng ng

xc nh c chui m v) tng ng vi chui sng m.

Qu trnh hun luyn s hun luyn cho tng m hnh m v HMM ng vi

tp hp tt c cc chui sng m c gn nhn tng ng vi n.

Cc tham s c c lng cho HMM l xc sut chuyn trng thi ttrng thi i sang trng thi j gia cc trng thi ca HMM aij cc tham s ca tng

trng thi vector trung bnh v vector hip phng sai .

Trong nhn dng h thng s da vo cc m hnh HMM hc c v m

hnh ngn ng(language model) hay vn phm (grammar) v p dng cc chin

Sngm

Rt

Trch

c

trngFile gn

nhn

ctrng

HMMPrototype

Tinm v

Hun

luyn Sngm

Hnh 3.3.1 S hun luyn m hnh HMM


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lc tm kim tm kim chui cc m tit tng ng vi chui sng m a

vo. Chi tit nh trong hnh di y.

Ta c th thy lc hun luyn th chng ta hun luyn trn m hnh m v,

cn lc nhn dng th chng ta nhn dng trn m tit. Chin lc tm kim c

xy dng da trn thut ton Viterbi.

3.4.2.Cc thnh phn c bn ca h thng nhn dng ting ni da trnHMM v mi lin h gia chng

Chng ta xem xt phn ct li ca HMM p dng vo nhn dng ting ni,

by gixem xt n cc thnh phn c bn ca h thng nhn dng da trn

HMM. Cc thnh phn ny bao gm:

1. Rt trch c trng d liu

2.

M hnh m hc3. M hnh ngn ng

4. Chin lc tm kim

Rt trch c trngs bin i cc chui tnh hiu s sng m thnh chui

cc vector quan st O= o1, o2,, oT. Mi vector Ot s c t10 n 40 thnh phn,

Hnh 3.3.2 S nhn dng tm hnh HMM hun luyn

Sng m

Rt

Trch

c

trngNg php

ctrng

Cc m hnh

HMM hunluyn

Tinm v

Nhndng

Tnhndngc


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lu gi cc thng tin ca sng m. Qu trnh rt trch c trng sc gii thiu

phn sau.

M hnh HMM m hcdng cc m hnh HMM m hnh ha cc mu

sng m ca mt n v ting ni. n v ny c th l t (m tit) hoc cc nvdi t (m v). Mi HMM trong h thng m hnh ha cc th hin thc t

ca mt n v ting n. i khi cc n v m hnh ha (trong hun luyn) li

khc so vi cc n v trong nhn dng. V d, trong hu ht cc h thng nhn

dng ting ni, n v trong m hnh ha l phones (l m v v mt sn v

khng phi l ting ni), hay triphones(cc m v ph thuc ng cnh), trong khi

n v trong nhn dng li l t (hoc m tit). Nguyn nhn ca vic ny l

vn k thut. Do slng t l rt ln (i vi ting Vit l khong 8000 t)nn vic phn bit trc tip trn cc t l khng th. Tuy nhin cc t (hoc m

tit ) li c cu thnh t mt sn vc bn l m v, c slng nhhn

nhiu. V vy hu ht cc h thng nhn dng sm hnh ha cc n vdi t

(sub-word) nh m v trong khi s nhn dng cc t da vo tm kim cc

chui m vtng ng ca n. Cc h thng nhn dng nh vy gi l h thng

nhn dng da vo cc n vdi t (sub-word based system).

S lin h gia cc trng thi ca HMM v khng gian m hc (acoustic

space) chnh l hm xc sut quan st b (observation probability function), c 2

dng c bn: ri rc (discrete-density) v lin tc (continuous-density). Do s

c 2 loi m hnh HMM l m hnh HMM lin tc (CDHMM) v m hnh HMM

ri rc (DDHMM). H thng DDHMM s dng nhiu b nhhn nhng li tnh

ton nhanh hn CDHMM. Cc tham s ca DDHMM l CDHMM u c tnh

bi gii thut Baum-Welch.

M hnh ngn ngtrong nhn dng ting ni th hin s chuyn tip c th

xy ra gia cc t (m tit). M hnh ngn ng cha cc thng tin nh cc rng

buc c php ca ngn ng t nhin. Trong ng dng c 2 loi m hnh ngn ng

thng c s dng, l m hnh ngn ng lut thng k v m hnh ngn

nglut quyt nh. M hnh thng k thng c s dng l m hnh word n-


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gram. V d, m hnh 2-gram xc nh xc sut ca t hin hnh ph thuc vo t

trc n. Tham s ca cc m hnh trn c thc xc nh da vo d liu vn

bn ca cc c sd liu sng m (vn bn m t dy cc t trong d liu sng

m). Xc sut chuyn dch gia cc t khng thy c qua qu trnh hun luyndo chng ta c th cho chng cc gi tr nh nhm cho php xc nh cc xc

sut chuyn dch gia cc t lc kim tra chng trnh trn d liu test trong

corpus (corpus l d liu bao gm ting ni c thu m v cc file vn bn ni

dung tng ng vi d liu ). Loi m hnh ngn ng cn li l m hnh ngn

ng lut quyt nh, n xc nh tt c cc dch chuyn hp l gia cc t. Cc

lut ny c thc hun luyn t cc d liu text hoc c thc to ra da

vo cc h thng nhn dng khc trong mi cu s tun theo cc qui tc ngphp nht nh.

M hnh ngn ng c mt vai tr ln trong nhn dng ting ni. l v s

hn ch ca cc m hnh m hc trong nhn dng ting ni v slng kt hp

gia cc t l rt ln trong khi nu c m hnh ngn ng chng ta c th hn ch

slng kt hp ny xung rt nh. Do khng gian tm kim s gim xung

ng k nn tc v chnh xc ca nhn dng stng ln rt nhiu, c bit

khi chng ta lm vi slng t ln. S thit k, cu trc ton hc ca m hnhngn ng, cc phng php xc nh cc tham s ca chng, stng hiu qu

ca h thonosgs nhn dng c trnh by trong nhiu ti liu v m hnh ngn

ng (v d, Shih et al, 1995).

Thnh phn cui cng, chin lc tm kim, cng l mt thnh phn rt quan

trng i vi chnh xc, hiu qu ca h thng, v i vi s cn bng ca c 3

thnh phn trn. N trthnh mt thnh phn v cng quan trng khi slng t

nhn dng rt ln. Khng gian tm kim ny bao gm cc s kt hp ca tt c

cc lin kt c th gia cc m v v gia cc t trong nhn dng trn tin ln.

Cc thut ton tm kim c thit k ph thuc vo tng cng vic nhn dng

ting ni c th. Thut ton thng c s dng nht trong tm kim l

thut ton Viterbi.


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38


CHNG 4

TIN XL TN HIUTRCH C TRNG XY DNG

M HNH HMM

4.1.Tin xl ting ni4.1.1. ngha ca tin xl ting ni

nhn dng ting ni, trc tin cn thu ting ni. Cht lng ting ni thu

c cng tt th nhn dng cng chnh xc. Tuy nhin trn thc t, d l trong

phng th nghim hay mi trng sinh hot hng ngy, ngi ta vn chthu c

ting ni km theo nhiu tn hiu khng mong mun khc, bao gm ting n (ting

qut my, xe c, ), nhiu (ting nhp mi, ting th, nhiu do in t), tingvang, Ngoi ra, m thanh thu c c th b bp mo do thit b (microphone,

card m thanh,), m thanh qu to, qu nh, V vy, qu trnh tin x l tn

hiu c a vo qu trnh nhn dng ting ni (ngay sau giai on thu m)

nhm a cht lng m thanh ln cao nht c li cho qu trnh nhn dng sau ny

(khi hc mu, nhn dng,)

V mt k thut, qu trnh tin x l s p dng cc phng php my hc,thut gii hoc p dng mt hay nhiu b lc ln tn hiu ting ni va mi thu

c.

Gi:

Yi l tn hiu thu c ti thi im i

Xi l tn hiu thun ting ni ti thi im i

Ni l tn hiu khc (nhiu, tn hiu lm mp ting) ti thi im i

Ta c:

i i iY X N (4.1)


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Trong , Ni c th l tp hp ca M ngun tn hiu nhiu khc

nhau:

Nh vy, u vo ca qu trnh tin x l l dy tn hiu m thanh thu c

c chiu di k:

Y = { Y1, Y2,..., Yk}

V u ra l dy tn hiu ting ni l tng c cng chiu di:

X = { X1, X2,..., Xk}

Thc hin tt qu trnh tin x l snng cao ng k cht lng nhn dng.

Tuy nhin trn thc t, qu trnh tin x l ch hn ch nhng nh hng khng

mong mun tc ng xu n kt qu nhn dng ch khng th trit tiu ht c

chng.

4.1.2.Mt s cng vic trong tin xl ting ni

4.1.2.1.Lm ni tn hiu (preemphasis )Thc hin mt b lc thng cao nhm hn ch vic gim i cng tn hiu

trong d liu ting ni. Nh tn gi ca n, b lc thng cao gi li cc thnh

phn c tn s cao v loi bi cc thnh phn c tn s thp. Trong ting ni,

cc thnh phn c tn s cao mang nng lng t hn nhiu so vi cc thnh

phn c tn s thp, nhng nhng vng ny li lu gi mt phn tn hiu quan

trng ca ting ni, v vy chng ta stng cng tn hiu trong vng tn scao, lm cn bng tn s gia cc vng. Ngi ta cn gi qu trnh ny l lm

phng tn hiu ting ni. Qu trnh lc c thc hin nh sau:

ng vi mi gi tr Xi trong chui d liu u vo X = {X1, X2, , Xk},

p dng cng thc:

M

i ij N N j (4.2)


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Yi = Xi + a*Xi-1

Trong ,

Y = {Y1, Y2, , Yk} i = 1..k: chui tn hiu c xl

i xc nh mu thi im i

l h s lm ni, thng c chn t 0,95 n 0,97. H s lm ni a

cng cao, thnh phn c tn s thp b loi i cng nhiu.

4.1.2.2.Lc ting n Thut ton Trm phphi tuyn (Nonlinear Spectral SubtractionNSS)

Thut ton NSS s dng n t l SNR (Signal to noise ratio) ph thuc tn

s. S dng php tr phi tuyn, h s tr s gim cc thnh phn ph c t l

SNR cao v tng cc thnh phn ph c t l SNR thp. Thm vo , m hnh

ting n c mrng bng cch s dng c ph ting n trung bnh v ph ting

n vt ngng. NSS c th hin bng cng thc sau:

Hnh 4.1 Sng m ca thai trc v sau khi c lm phng

^

( ) .i i

X H Y

(4.3)

(4.4)


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Trong ,Hi() ph thuc vo c lng lm trn ca phcng ting

n, |..

Y ()|, v h s tr phi tuyn i(),

H s tri() c tnh nh sau:

Vi

l hng s co gin ph thuc vo khong i

Khong bin thin ca i :

3i i iN N

Thut ton c lng MMSE (MMSE Estimator)

Ephraim v Malah xut thut ton ny p dng cho cc thnh phn

bin ph ting n ngn k. Trong phng php ny, cc thnh phn ph

ca ting ni v tin n c m hnh thnh cc bin ngu nhin Gaussian.

Thut ton c lng thnh phn bin ca ph th k bng b lc sau:

i

i

i

Y

N

i i

i

i

H

H

Y

(4.5)

ax

1

i M i

i

i

m N

(4.6)


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0 1exp 12 2 2 2

k k k k

i k k k

k

v v v v H v I v I

Trong , 0 2kv

I

v 1 2k

vI

l hm Bessel hiu chnh th 0 v th 1.

Vk c tnh nh sau:

1

kk k

k

v

k v

k l cc t l SNR a priori v a posteriori ca thnh phn ph thu k.

4.2.Rt trch c trng4.2.1.Gii thiu

Tn hiu ting ni thu c t micro vn c kch thc ln. My tnh c

nhn khng c tc v b nhcho qu trnh nhn dng lng d liu ln

. gii quyt vn ny, ngi ta ch trch ra v x l nhng thng tin

cn thitnht t dy tn hiu thu c. Cc tn hiu trch ra c gi l c trng

ca dy tn hiu gc. c trng ny phi tho nhng iu kin sau: Nhhn rt nhiu so vi tn hiu gc ( khng chim b nh, gim

thi gian khi xl,).

Vn gia li nhng c im quan trng nht ca dy tn hiu ban

u.

C nhiu dng c trng, c th chia thnh 3 nhm sau:

Nhm 1:

c trng trch ra nh m phng theo m hnh b my pht m ca con

ngi. Cc c trng nhm ny s dng phong php d bo tuyn tnh rt

t trng. Cc phng php thng dng l: Linear Predictive Coding

(4.7)


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LPC, Perceptional Linear Prediction (PLP),

Nhm 2:

c trng trch ra nhda trn kh nng cm nhn m ca thnh gic conngi. Cc c trng nhm ny s dng phng php phn tch cepstral1 v

ph m (spectral) (cn gi l cc phng php dy b lc). Phng php

thng s dng l Mel Frequency Cepstral Coding (MFCC).

Nhm 3:

Mt s cc c trng m hc khc v cao , ngiu, du nhn: thch hp

cho nhn dng ngn ngang ni, thanh iu, tm trng ngi ni, .

Cc c trng nhm 3 t c dng trong vic nhn dng m tit . Ngi ta

dng ch yu cc c trng nhm 1 v nhm 2.

4.2.2.Mt sphng php trch c trng4.2.2.1. Phng php m ho dbo tuyn tnh(LPC)Phng php m ho d bo tuyn tnh rt ra cc h s d bo tuyn tnh

(Linear Prediction Coefficients). LPC l mt k thut c s dng kh rng ri vn trch ra c m hnh tn hiu ting ni tng i tt v chy tng i nhanh

hn so vi cc k thut dng dy b lc. (Tuy nhin, vi cc my tnh ngy nay,

tc khng cn l vn ng quan tm).

Trong phng php ny, ngi ta hng ginh:

- Dy thanh m c lp vi b my pht m

- B my pht m c cu to tuyn tnh

Trong mi trng cng hng ca b my pht m tuyn tnh, gi tr ca tn

hiu hin ti s l thuc vo cc gi trtrc , tc l tn hiu s(t) ti thi im t


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c biu din bng mt phng trnh tng ca tch p gi tr tn hiu trc

trong frame v cc h s:

1 21

( ) * ( 1) * ( 2) ... ( ) ( )

p

p ii

s t a s t a s t a s t p a s t i

Chng ta khng th tm ra dy s ai chnh xc m ch c thc lng tm ra

gi tr gn nht.

Ginh v cc tnh gi tr tn hiu nh trn l khng chnh xc v tnh cng

hng trong c quan pht m bin thin chm theo thi gian. V vy, mt gi tr

li sc cng thm vo kt qu:

1

( ) ( ) ( )p

i

i

s t a s t i e n

Hm truyn c xy dng bng b lc ton cc, c dng:

0

1( )

pi

ii

H z

a z

Trong , p l slng cc v a0 1 v cc h s lc {ai} c chn sao cho

sai s don bnh phng t gi tr ti thiu. C 2 phng php c s dng:

t tng quan v hip phng sai. Phng php hip phng saic s dng

trong tn hiu tun t. Chng ta chxem xt n phng php ttng quan: ng

vi mi frame, p+1 h stng quan u tin c tnh nh sau:

1

( ) ( 1)N i

i

j

r s j s j

vi 0 i p

(4.8)

(4.9)

(4.10)


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Sau , cc h s lc c tnh ton quy s dng cc h stng phn.

Gi E l li dbo. Ban u, E = r0, v gi k(i-1) v a(i-1) ln lt l h stng

phn v h s lc cho b lc th (i-1). B lc th (i) c thc tnh qua 3 bc:

Bc 1: To cc h stng phn mi:

( ) ( 1)i i

j jk k

vi 1 1j i

( ) ( 1) ( 1)/i i ii i j i jk r a r E Bc 2: Cp nht nng lng don:

( ) ( ) ( ) ( 1)1i i i ii i E k k E

Bc 3: Tnh cc h s lc mi:

( ) ( 1) ( ) 1i i i i

j j i i j

a a k a

vi 1 1j i

( ) ( )i i

i ia k

Cc h s lc c tnh qua p bc lp.

4.2.2.2.Phng php M ho cepstral tn s Mel (MFCC)

Davis v Mermelstein a ra thut ng h s cepstral theo tn s Mel

(Mel- frequency Cepstral Coefficients - MFCC) vo nm 1980 khi h kt hp

cc b lc cch khong khng u vi bin i Cosine ri rc (DCT) thnh

mt thut ton u-cui ng dng trong lnh vc nhn dng ting ni lin tc.

(4.11)

(4.12)


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Phng php MFCC l mt trong nhng phng php s dng dy b lc.

Phng php ny s rt ra c trng thng qua 2 giai on. u tin, nng

lng dy b lc hp c xc nh bng cch s dng mt dy b lc Mel

scale. Sau , cc nng lng ny c m ho bng php bin i Fourier (haycc php bin i tng t)y chnh l giai on phn tch cepstral.

Qu trnh trch c trng MFCC ni chung qua cc bc sau:

Lm ni tn hiu (xem phn phn tin x l)

sf[n] = preemphasis(s[n])

Tn hiu c nhn vi cc ca s chng lp v chia ra thnh cc

frame c chiu di 20~30 ms vi khong chng lp gia cc ca s t

10~15 ms.sf[n] = s[n].w[n]

w[n] thng l ca s Hamming c gi tr:

0.54 0.46 os(2 / ) 0

w0 erwise

c n N n N n

oth

Php bin i Fourier (DFT, FFT, ) c p dng cho mi frame

tnh ph tn hiu, sau ly log

Sf() = log|DFT{sf[n]}|

24 dy b lc tam gic vi khong cch xp x logarit (gi l dy b

lc Mel) c p dng cho sf (). Nng lng trong cc dy ny

c tch hp cho ra 24 h s trong ph. Dy b lc Mel-scale bao

gm mt dy cc b lc tam gic chng ln nhau vi tn sv rng

dy tnh theo t l tn s Mel. T l tn s Mel, ging nh t l Bark s

dng cho phng php PLP, c da trn nhng kt qu nghin cutm l tcon ngi. Mi khong ngh trong t l Mel ng vi mt cao

tng i ca mt tone m con ngi cm nhn. Thc t kim

nghim c vi cch khong nh vy ca dy b lc, t l nhn dng

ng c nng ln. Tip theo, cc h scepstral c tnh t php

(4.13)

(4.14)

(4.15)


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bin i Cosine ri rc (DCT).

c= DCT{S()}

12 h su tin (tri h s th0) chnh l cc c trng MFCC.

4.2.2.3. Phng php M ho cepstral tn s Mel da trn LPC(MFCC)

Phng php ny ging nh phng php MFCC. im khc bit l sau

bc phn chia ca s, ph tn hiu c tnh thng qua php bin i d bo

tuyn tnh LPC thay v dng cc php bin i Fourier.

4.2.2.4. Cc h s delta (D) v h s gia tc (A)Hiu sut ca mt h nhn dng ting ni c th tng ln ng k nu

Tn hiu ting ni

Phn chia ca s

Lm ni tn hiu

FFT

Dy b lc Mel

Log|tn hiu lc Mel|

DCT

Cc c trng MFCC

LPC

Dy b lc Mel

Log|tn hiu lc Mel|

DCT

Cc c trng MFCC da

Hnh 4.2 S ca b lc MFCC da trn bin i d bo tuyn tnh vcc bin i Fourier

(4.16)


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chng ta a thm gia s thi gian vo b tham stnh cbn. y, chng ta

s xem xt h s D (delta) v h s A (accelerator).

H s D l h sc c do tnh o hm bc nht ca c trng gc, h s

gia tc A c c nhtnh o hm bc hai ca c trng gc. H s A khng thdng ring l mt mnh. H sdelta c tnh da vo cng thc truy hi sau:

1

2

12

t t

t

c cd

trong , dt l h s delta ti thi im t c tnh da theo cc h stnh ct+

v ct-.

Do phng trnh trn ph thuc vo cc gi tr tham s ting ni s dng

v cha s dng nn chng ta cn tinh chnh phn u v cui ca li ni. Thng

thng, chng ta nhn i vector u tin hoc vector cui cng. Mt cch khc l

s dng im khc bit vtr u u v cui ting ni:

1 ,t t td c c t

v

1,t t td c c t T

Trong , T l chiu di d liu.

Nu s dng h s delta v h s gia tc trong c trng, chng c p dng

cho ton b cc c trng gc, bao gm c nng lng nu c. Trong vi ngdng, nng lng tuyt i khng ng vai tr quan trng, nhng nhng trch

on v thi gian ca nng lng th quan trng.

4.3.So snh cc phng php trch c trng

(4.17)


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Phng php LPCPhng php MFCC da trn LPC

Spectral LPC dng b lc t l Mel (MFCC da trn LPC) c hiu sut

tt hn mt cht so vi spectral LPC d bo tuyn tnh. Nguyn nhn c th

do hiu ng lm mt vng tn s cao ca b lc t l Mel, lm gim i cc yut cao tht thng trong vng tn s cao bng cch nng cao bng thng ca

cc dy b lc Mel.

Phng php MFCC da trn LPCPhng php MFCC da trn FFT

MFCC da trn LPC c khuynh hng ph thuc ngi ni, do , thch

hp hn cho cc cng vic nhn dng ngi ni.i vi ting ni khng b pha

tp ting n hoc ting ni ging ting ni hc mu, phng php LPC c hiu

sut km hn FFT (c2 u dng b lc t lMel), nhng i vi ting ni mitrng n o hoc khng ging dng ting ni hc mu, c lng spectral

LPC c hiu sut cao hn.


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CHNG 5

THC HIN CHNG TRNH MU

5.1Gii thiu v qu trnh thc hin chng trnh

Mc ch ca nhm thc hin l thc hin mt chng trnh c kh nng

nhn dng c mt s cu lnh ngn nh Gi H, Gi Khnh, Bm 0,

Bm 1, nhm th hin chi tit cc qu trnh nhn dng ting ni da trn m

hnh HMM v vi mc ch nhn dng cc cu lnh iu khin my tnh.

Nh trnh by phn l thuyt vic nhn dng c thc hin l nhn

dng m v ch khng phi nhn dng t, do slng m vt hn rt nhiu so vislng t, m bo tnh kh thi trong thc hin chng trnh.Tuy nhin v phn

tin m v cho t vng ting Vit cha c mt chun phin m no nn nhm

thc hin ti thc hin phn chia m v cc t theo m hnh sau:

T

m u Nguyn m m cui

V d tKhnh sc chia m vthanh KH - -NH.

Thm na, do cc cng c trong HTK (tnhin a vo HTK m cha gii

thiu vn v ni s qua dng n lm g) khng h trm Unicode nn vic nh

ch ting vit sc quy c theo kiu g Telex. V d:

AS

UOW

OOJ

Hnh 5.1 M hnh hn chia m v cho t


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Trn y l mt squy c ca nhm lm ti khi thc hin chng trnh

mu. thc hin c chng trnh th chng ta cn mt ci t v cu hnh mt

schng trnh, c trnh by phn tip theo.

5.2Ci t cc chng trnh cn thitQu trnh thc hin cn cc chng trnh sau:

HTK toolkitb cng c xy dng m hnh HMM

Cygwinchng trnh to mi trng Linux trn windows.

Audacitychng trnh thu m trn PC cho php xem v chnh sa

waveform.

Julianmt engine nhn dng ging ni.

Qu trnh ci t cc chng trnh trn c hng dn k ti a ch

http://www.voxforge.org/home/dev/acousticmodels/windows/create/htkjulius/tutori

al/download

Sau khi ci t v cu hnh ng cc chng trnh trn theo hng dn,

chng ta bt u cc bc thc hin chng trnh.

5.3. Qu trnh thc hin chng trnh muCc bc thc hin chng trnh bao gm:

1. Chun b d liu

a. Thu d liu

b. Gn nhn d liu

c. Rt trch c trng2. Xy dng m hnh ngn ng

3. Hun luyn

a. Khi to tham s cho HMM

b. Hun luyn trn m hnh monophone


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4. Xy dng chng trnh nhn dng

5.3.1.Chun b dliu5.3.1.1. Thu dliuCng c HParse ca HTK c dng pht sinh cc cu ngu nhin (bng

vn bn), sau sthu m cc cu ny, lu mi cu vo mi file ring bit. Cc

file m thanh c lu nh dng WAV (Microsoft 16 bit PCM) vi cht lngnh sau:

nh dng tc ly muDefault Sample Rate Format, l 48000Hz

nh dng ly muDefault Sample Format l 16bit Knh m thanhChanel : Mono

Thao tc chnh cht lng m thanh c thc hin trong giao din Audacity.

Tool HParse ca HTK c th pht sinh cu ngu nhin, tuy nhin ta phi cung cp

danh sch t vng cho n. Danh sch t vng ny t nht phi bao gm cc t m

ta cn nhn dng. File cha cc cu c pht sinh c dng nh sau:

Trong qu trnh thu m, cn gim thiu tin n (hi th, xe c, qut) v c

khong ngt ngn gia cc t. u v cui cu c vng lng nh du.

Hnh 5.1 File cha cc cu c pht sinh ngu nhin


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5.3.1.2.Gn nhn dliuChng ta ch cn to cc file m t th t cc m tit trong cu v dng t

in m v chuyn chui m tit thnh chui m v. Trong lc gn nhn, chng

ta nn thm m vsilence vo gia 2 m tit. iu ny lm tng hiu qu ca qu

trnh nhn dng ln nhiu, v thc t l gia 2 m tit thng c khong silence.

Nhng nu khng c m v sillence gia 2 m tit th cng khng nh hng ti

qu trnh hun luyn. Sn phm ca giai on ny l 2 file phones0.mlf v

phones1.mlf (mlfmaster label file) cha tt cvn bn ca cc cu c thu m

nhng c phin m sang mc m v.

5.3.1.3. Rt trch c trng dliuGiai on ny l giai on chuyn d liu sng m sang d liu c trung

MFCC(Mel-frequency cepstral coefficientsh s cepstral tn s Mel). Cng c

c dng cho thao tc ny l HCopy. HCopy thc hin vic chuyn i theo cc

thng sc chng ta cung cp, c thtrong ti nh sau:

# Coding parameters

TARGETKIND = MFCC_0

TARGETRATE = 100000.0SAVECOMPRESSED = T

WINDOWSIZE = 250000.0

USEHAMMING = T

PREEMCOEF = 0.97

NUMCHANS = 26

CEPLIFTER = 22

NUMCEPS = 12

ENORMALISE = F

Hnh 5.2 Cu hnh chng trnh trch

c trng


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D liu sng m c thu di tn s ly mu 16000 mu /giy, kch

thc mi mu l 16 bit.

Kch thc mi ca s l 25 ms. chng lp ca cc ca s l 15 ms.

S dng dy b lc s dng c 26 knh. C th hiu qua v cu hnh trch ctrng trn l: tham s ch l MFCC s dng Co l thnh phn nng lng,

khong thi gian ly khung d liu l 10ms (HTK s dng n v 100ns), outut

c lu dng nn c crr checksum. Bin i FFT s dng ca s Hamming

(USEHAMMING = T(True)) c th t tin nhn u tin s dng h s l 0.97

(PREEMCOEF = 0.97). Ton b qu trnh s dng HCopy c trnh by nh

trong Hnh 5.3.

5.3.2.Khi to m hnh HMM

HDMan

WaveFormFile

sample1.wav

sample2.wav

Configurationfile (config)

Script File

(cha danh sch filengun v file ch)

MFCC file

sample1.mfc

sample2.mfc

Hnh 5.3 Trch c trng vi HDMan


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Nh gii thiu trong gii thut Embedded Training, khi to HMM

cho cc m hnh l rt quan trng, n nh hng n tc hi t ca thut

ton, v s chnh xc ca thut ton.

Trong phm vi ti nhm thc hin s dng phng php Flat start khito tham s cho HMM. y l phng php khi to trn d liu khng gn nhn

ca HTK. tng ca cch khi to ny l da vo cc d liu hun luyn

c a vo, chng ta s khi to cc HMM sao cho chng c vector trung

bnh v hip phng sai bng nhau v bng vi vector trung bnh ton cc v

vector hip phng sai ton cc ca d liu hun luyn.

Vic u tin cn lm trong giai on hun luyn l nh ngha mt m hnh

nguyn mu. Cc tham s ca m hnh ny khng quan trng, mc nh chnhca n l nh ngha mt m hnh cu trc lin kt. M hnh nguyn mu c

cung cp trong HTK c dng

~o 39

~h "proto"

5

2

39

0.0 0.0 0.0 ...

39

1.0 1.0 1.0 ...

3

39

0.0 0.0 0.0 ...

39

1.0 1.0 1.0 ...

4

39

0.0 0.0 0.0 ...

39

1.0 1.0 1.0 ...

5

0.0 1.0 0.0 0.0 0.0

0.0 0.6 0.4 0.0 0.0

0.0 0.0 0.6 0.4 0.0

0.0 0.0 0.0 0.7 0.3

0.0 0.0 0.0 0.0 0.0

Hnh 5.4 M hnh nguyn mu trong HTK Book (proto)

Trong m hnh ny chiu di mi vector l 39 bao gm cc c trng c


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rt trch l MFCC_O (13 c trng). S dng thm 2 c trng na l bin

thin (13 c trng) v gia tc bin thin (accelerator) (13 c trng ). Nh

vy mi vector c trng s c 39 thnh phn.

5.3.3.Hun luyn m hnh HMMCng c thc hin hun luyn Embedded training trong HTK l

HERest. HERest s dng cc m hnh HMM va khi to v d liu hun

luyn hun luyn ra cc HMM m vc lp ng cnh monophone. M hnh

ca qu trnh hun luyn nh hnh di. Chi tit v thut ton hun luyn trn

d liu khng gn nhn m v Embedded training c gii thiu phn trn.

HERest s load cc m hnh HMM va khi to cha trong file hmmdefs

(file cha nh ngha cc m hnh HMM) trong danh sch m vmonophone0.

Qu trnh c lng tham s s s dng cc file hun luyn cha trong danh

sch file hun luyn trains.scp v cc chui cc m vtng ng nm trong file

Cc monophonec hun luyn

(cc hmmdef mi)

File gn nhn m v

(phone0.mlf)

HMM khito (hmmdef)

Danh sch HMM(monophones0)

Danh sch file hunluyn (trains.scp)

HERest

Hnh 5.4 M hnh hun luyn monophone dng HERest


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phone.mlf to ra cc HMM mi. Cc HMM c hun luyn c lu

trong th mc new_hmm. Chng ta s lp li s ln hun luyn nhiu ln n

khi hi t. Tiu chun nh gi hi t l xem s hi ca gi tr log_likelihood

trung bnh trn mi frame d liu hun luyn. Thng th s ln hun luyn lt 2 n 5 ln. Nu sbc lp hun luyn qu t th mc chnh xc ca cc

HMM khng cao. Nhng nu s bc lp qu ln, s xy ra tnh trng qu

luyn dn n mc tng qut ca cc HMM li b gim i. V vy chng ta

s phi quyt nh s lng cc bc lp sao cho hiu qu nht. Trong phm vi

ti, s ln hun luyn l 3, c lu trong th mc hmm3 tng ng.

i vi cc ngn nga m, tng chnh xc khi nhn dng, ngi ta

s tip tc tin hnh sa thm m hnh HMM cho sp, l khong thi gian dngngn gia cc m tit. Tuy nhin, ting Vit li l ngn ngn m, mi tcng

l mt m tit nn thao tc ny l khng cn thit. Nh vy, m hnh HMM

bc cui cng c th dng cung cp cho engine Julian thc hin nhn

dng.

5.3.4.Nhn dng bng JulianMc d Julian h trnh dng HMM ca HTK, tc l file hmmdef c c

bc trn c thdng c cho Julian. Tuy nhin, gii hn slng t

cn nghe nhm tng chnh xc, phi cung cp cho engine ny mt m hnh

ngn ng hoc mt file ng php cung cp cc lut lin kt gia cc t cho n.

Trong phm vi ti, vi slng t vng khng nhiu, nhm thc hin xy

dng cho Julian mt file ng php c ni dung nh sau:

S : NS_B SENT NS_E

SENT: CALL_V NAME_NSENT: DIAL_V DIGIT

Hnh 5.5 Ngphp dng trong chng trnh


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T vng ng vi cc nhn trong ng php c cung cp thng qu file

.voca nh sau:

% CALL_V

GOIJ g oij% DIAL_V

BAASM b aas m

% NAME_N

KHASNH kh as nh

HAF h af

THAAFY th aaf yDDAJT dd aj t

LINH l i nh

% DIGIT

KHOONG kh oo ng

MOOJT m ooj t

Nh vy, Julian sc gii hn nghe cc cu lnh dng Gi H, Gi

Khnh hoc Bm khng Bm Mt m khng chp nhn cc kt qukhc. iu ny nm trong mong mun s dng ca ngi dng. Nh vy, vi 3

file hmmdefs, mygram.grammar, mygram.voca, Julian c th thc hin vic nhn

dng. Nhng trc khi chy Julian, cn phi cu hnh engine nhn ng cc

file ngun to. C thnh sau:

## Grammar definition file (DFA and dictionary)

-dfa mygram.dfa-v mygram.dict

## Acoustic HMM file

-h hmm3/hmmdefs

-smpFreq 48000 # sampling rate (Hz)

Hnh 5.6 cu hnh cho Julian (file julian.jconf)

Cui cng, bt u chy Julian vi dng lnh sau:$julian -input mic -C julian.jconf

5.4. nh gi kt quv hng pht trin5.4.1.Kt qu


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Vi vn t bao gm cc t /GI/ /BM/ /H/ /KHNH/ /THY/ /T/

/LINH/ /KHNG/ /MT/ /HAI/ /BA/ /BN/ /NM/ /SU/ /BY/ /TM/

/CHN/ /MI/, chng trnh cho chnh xc 86% trong iu kin yn lng v

cu lnh pht ra r rng.Nu mrng slng t vng ln c thp ng c cc ng dng lnh bng

ging ni c bn.

5.4.2.Nhn xtMc d nhn dng tng i chnh xc cc t vng trn, tuy nhin vn t

vng m chng trnh s dng cn t, cha kim tra c chnh xc khi pht

trin vi slng t vng ln.

Mt vn khc l ti ch mi dng li bc xy dng m hnh HMM mc monophone m cha xy dng c mc triphone, nn chnh xc

cha cao.

5.5.Kh khn v hng pht trini vi vic xy dng chng trnh nhn dng cho ting Vit, kh khn ln

nht l cha c nhng cng trnh nghin cu mang tnh chun mc v ng m

ca ting Vit, do khi p dng vo HTK, bn thn nhm thc hin cng p

dng cc k thut mc cm tnh, cha m bo c s chnh xc.Ngoi ra, chnh v y cng l mt lnh vc kh mi mnc ta nn rt t

ti nghin cu su vlnh vc ny, v vy m vic thc hin bt u tcc

ti dnh cho ting Anh, mt ngn ng kh khc bit vi ting Vit, nn mt s

cng c ch chnh xc cho ting Anh.

Hng pht trin ca chng trnh l tng slng t vng, xy dng c

b tin pht m chun v chnh xc theo m hc (rt quan trng v khi pht

trin s lng t ln, khng th phin m bng tay m phi lm tng), xy

dng c m hnh triphone tng chnh xc. Sau khi t c chnh xc

mong mun, c th tip tc hun luyn vi nhiu ging khc nhau, to thnh mt

chng trnh nhn dng c lp ngi ni, tng tnh kh dng ca chng trnh.


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TI LIU THAM KHO

Ting Vit:

[1] inh L Th - Nguyn Vn Hu, C cu ng m TingVit, NXB Gio Dc,1998

[2] Thi Hng Vn, Lun n thc s, khoa Cng ngh thng

tin, i hc Khoa hc T nhin, 2000

[3] Xun tV Vn Tun, Lun vn tt nghip khoa

Cng nghthng tin,i hc Khoa hc T nhin, 2003

[4] ng Thi Dng H Giang Hi, lun vn tt nghip

khoa CNTT, H Khoa hc t nhin, 2004

Ting Anh:

[5] X. HuangSpoken Language Processing: A Guide toTheory, Algorithm and System Development

[6]Foundations of Statistical Natural Language Processing" byManning & Schtze. Chapter 9, Markov Models

[7]Lawrence R. Rabiner, A tutorial on Hidden Markov Models and Selected Applications in Speech Recognition,IEEE, 1989


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